age = input('enter your age:')
try:
    age = float(age)
except ValueError as ve:
    # ValueError是指定类型的错误，可以通过元组指定多种类型的错误
    # 例如：except (ValueError, FileNotFoundError) as e:
    print(ve)
else:
    if age > 18:
        print('you can enter')
    else:
        print('please leave')
